The present invention relates to an improved single line grab system.
Conventional "2-line grabs," require both a holding line and a closing line. A grab, such as a bucket having two parts connected by a central pivot, may be raised and lowered when a brake is in a released position so that the holding line moves freely through the brake. To open the bucket, the brake is applied to the holding line to create tension. As the closing line is fed, the bucket pivot lowers and the bucket opens. Conventional "2-line grabs" are difficult to operate in that they usually require the operator to use multiple clutches, brakes, and a throttle. One such "2-line grab" is disclosed in U.S. Pat. No. 4,528,987 to Zoudlik.
Traditional "single line grabs" use a single line to raise and lower the bucket. One method traditionally used to open/close the bucket is a "bump and go" method in which the bucket remains closed until it "bumps" a surface such as the ground at which point it opens. The bucket is closed by raising the bucket off the surface. One such "bump and go method" is disclosed in U.S. Pat. No. 3,934,917 to Paxton et al. The "bump and go" system does not allow the load in a bucket to be emptied from an elevated position, and thereby requires additional time to lower the load prior to opening the bucket.
An alternate method traditionally used to open and close a bucket in a single line grab is to include a hydraulic system which opens and closes the bucket. One problem with hydraulic systems is that they often leak (which contaminates the contents of the bucket). Another problem with hydraulic systems is that they generally cannot be used under water.
U.S. Pat. No. 3,036,393 to J. Baird, Jr. discloses an alternate "single line" hoisting bucket that includes a clamshell grab suspended by a single line. A second line, however, is used to release the clamshells. More specifically, the Baird device requires an operator to pull a second line to release a cocker hook from a sleeve portion of a pivot shaft between the clamshells. The Baird device also requires a counterweight assembly block which lowers the cocker hook to engage with the pivot shaft and raises when the cocker hook is not engaged.
Other patents such as U.S. Pat. No. 226,557 to W. H. Seward, U.S. Pat. No. 376,242 to F. B. Barrows, U.S. Pat. No. 1,301,626 to W. E. Watters, and U.S. Pat. No. 1,869,989 to W. M. Venable, disclose devices which, like the above described apparatuses, are "bump and go" systems, require additional lines or release apparatus, include complicated raising and lowering assemblies, or otherwise are needlessly complicated.